Sheet feeding device utilizing vibration waves

ABSTRACT

There is disclosed a sheet feeding device having at least two vibration members pinching a sheet, which is frictionally driven by the travelling vibration waves generated in the vibration members. The device is further provided with a detector for detecting the state of vibration of the vibration members and generating a signal corresponding to the phase difference between the vibrations. The signal is used for correcting the vibration state of the vibrations members, thus significantly reducing the unevenness in the sheet feeding.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device adapted for usein computers, copying machines, printers, facsimile apparatus, wordprocessors, typewriters or the like, and more particularly to a sheetfeeding device utilizing a travelling vibration wave.

2. Related Background Art

A sheet feeding device utilizing travelling vibration wave has beenalready disclosed for example in the Japanese Laid-Open Patent Sho59-177243. In said device, the sheet feeding is achieved by supporting asheet between a pair of vibration members composed of an elasticmaterial and pressed each other by a suitable pressure, and generatingtravelling vibration waves in said vibration members. On each vibrationmember there is adhered or pressed two groups of electromechanicalenergy converting elements such as piezoelectric elements, which arearranged with a phase difference of an odd multiple of λ/4 between saidtwo groups, and, within each group, with a pitch of λ/2 and withalternating expansion-contraction polarity. One of said groups ofpiezo-electric elements on each vibration member is given an AC electricfield of a frequency in the vicinity of specific frequencies of thevibration members (in practice the specific frequency of eithervibration member), while the other of said groups of piezo-electricelements on each vibration member is given said AC electric field with aπ/2 phase shift achieved by a π/2 phase shifter, thereby generatingtravelling vibration waves in said vibration members symmetrically withrespect to the sheet feeding plane. A travelling vibration wave in eachvibration member causes an elliptic movement in each point on a surfaceof said member opposite to the piezo-electric elements, and the sheetfeeding is achieved by said elliptic movement of each point on mutuallyopposed faces of the vibration members, symmetric with respect to thesheet feeding plane, through friction between the sheet and thevibration members, and a change in the sheet feeding speed can beachieved for example by a change in the amplitude of the travellingvibration waves generated in the vibration members.

FIG. 3 schematically shows the principle of generating the sheet feedingforce by such travelling vibration wave, in which a sheet 9 is pinchedwith a suitable pressure between vibration members 1, 5 in whichtravelling vibration waves are generated as illustrated. Each point onthe surface of the vibration members 1, 5 moves generally along anelliptic trajectory. In the vibration member 1, when the travellingvibration wave moves to the right, as indicated by a white arrow, thesurfacial point moves clockwise along said elliptic trajectory. As thetravelling vibration waves generated in the vibration members 1, 5mutually have a spatial phase difference of 180°, the projectingportions of said waves toward the sheet 9 always proceed with mutuallyopposed relationship. Since each point on such projecting portions movesin a direction opposite to the proceeding direction of the vibrationwaves in the members 1, 5, there is generated a sheet feeding force tothe left, as indicated by a black arrow. In the recessed portions, thereis generated a sheet feeding force in a direction the same as theproceeding direction of the travelling vibration waves, but such feedingforce is weaker because of the smaller friction between the sheet andthe vibration members resulting from a lower pressure in such recessedportions than in the projecting portions. Thus the total sheet feedingforce is in a direction opposite to the proceeding direction of thetravelling vibration waves.

However, in such conventional sheet feeding device, the travellingvibration waves are generated in both vibration members with AC voltagesof a same phase even when the specific frequency of the vibration membervaries individually for example by fluctuation in the sheet thickness orvariation in the environmental conditions. Consequently a spatial phaseaberration or deviation may be generated between the vibration waves ofboth vibration members as shown in FIG. 4, due to a change in the loador in the environmental conditions, thus resulting in a fluctuation inthe sheet feeding amount.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a sheet feeding devicecapable of stable sheet feeding despite of a change in the load or inthe environmental conditions.

Another object of the present invention is to provide a sheet feedingdevice capable of stable sheet feeding, by maintaining the spatial phasedifference constantly at zero between the travelling vibration wavesgenerated in the vibration members supporting the sheet therebetween.

Still other objects of the present invention will become fully apparentfrom the following detailed description of the present invention.

According to an aspect of the present invention, the foregoing objectscan be attained by a sheet feeding device, in which a sheet to be fed issupported by pinching between a pair of vibration members composed of anelastic material and respectively provided with electromechanical energyconversion means and electric power supply to the electromechanicalenergy conversion means of said paired vibration members is socontrolled by power supply control means as to generate travellingvibration waves in said paired vibration members thereby feeding saidsheet with thus generated vibration waves, wherein said power supplycontrol means comprises a phase difference detecting unit for detectingthe positional phase difference between the travelling vibration wavesgenerated in said vibration members, and a control unit for controllingthe phase difference in time between AC voltages supplied to theelectromechanical energy conversion means of the vibration members insuch a manner as to bring the phase difference detected by said phasedifference detecting means to zero.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a first embodiment of the sheet feedingdevice of the present invention;

FIG. 2 is a block diagram of a second embodiment;

FIG. 3 is a schematic view showing the working principle of the sheetfeeding device; and

FIG. 4 is a schematic view showing a spatial phase aberration betweenthe travelling vibration waves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a first embodiment of the sheet feedingdevice of the present invention.

First and second metallic vibration members 1, 5 of an elongatedcircular shape with a certain thickness support a sheet 9 by pinchingtherebetween with a suitable pressure, and are respectively provided, onmutually distant faces thereof, with sections 3, 4, 7, 8 of two groupsof piezo-electric elements which are polarized in already known manner,so as to generate, in each vibration member, two standing waves mutuallydifferent by λ/4 in position (λ being wavelength of the vibration wave)or by 90° in time, thereby synthesizing a travelling vibration wave ineach vibration member. Said first and second vibration members 1, 5 areelectrically maintained at the ground potential. The first vibrationmember 1 is further provided with a detecting piezoelectric element 2for detecting the vibration state of the travelling vibration wavegenerated in said first vibration member 2, and the second vibrationmember 5 is likewise provided with a detecting piezoelectric element 6for detecting the state of the vibration wave in said second vibrationmember 5. There are further provided a known phase difference detector10 for detecting the phase difference in time, at a same spatialposition, of the travelling vibration waves generated in the first andsecond vibration members 1, 5 from the output signals of the detectingpiezo-electric elements 2, 6; a known low-pass filter (LPF) 11 foramplifying and integrating the output of the phase difference detector10; a known voltage-controlled phase shifter 12 for displacing the phaseof the output signal of an oscillator 13 to be explained later,according to the output signal of the low-pass filter 11; an oscillator13 for generating a reference signal for AC voltages to be applied tothe sections 3, 4, 7, 8 of the piezoelectric elements for forming thetravelling vibrations waves in the vibration members 1, 5; a first 90°phase shifter 14 for shifting the phase of the reference signal from theoscillator 13 by +90° or -90° according to a feeding direction switchsignal from an unrepresented means for setting the sheet feedingdirection; a second 90° phase shifter 15 for shifting the output of thevoltage-controlled phase shifter 12 by +90° or -90° according to saidfeeding direction switch signal; and power amplifiers 16, 17 foramplifying the output signals of the oscillator 13 and the first 90°phase shifter and those of the voltage-controlled phase shifter 12 andthe second 90° phase shifter 15 with suitable gains for supply to thesections 3, 4; 7, 8 of the piezo-electric elements.

In the sheet feeding device of the present embodiment explained above,if the phase in time at a certain spatial point of the travellingvibration wave formed in the first vibration member 1 is delayed, asshown in FIG. 4, from the phase in time of the travelling vibration waveformed in the second vibration member 5 at a point opposed to theabove-mentioned spatial point (it is assumed that the peaks of twotravelling vibration waves mutually meet as shown in FIG. 3 in case ofzero phase difference in time), the phase of the output signal of thedetecting piezo-electric element 2 for detecting the vibration state ofthe first vibration member 1 is delayed from that of the output signalof the detecting piezo-electric element 6 for the second vibrationmember. Thus the phase detector 10 provides a negative output signal,and the output signal of the low-pass filter 11 decreases. Consequentlythe output of the voltage-controlled phase shifter 12 is delayed inphase, so that the AC voltages applied to the piezo-electric elementsections 7, 8 of the second vibration member 5 are also delayed inphase. Thus the phase in time of the travelling vibration wave formed inthe second vibration member 5 is delayed until the peaks of saidvibration wave match those of the vibration wave formed on the firstvibration member 1, as shown in FIG. 3.

FIG. 2 is a block diagram of a second embodiment of the sheet feedingdevice of the present invention, wherein same components as those in theforegoing first embodiment are indicated by same numbers and will not beexplained further.

In FIG. 2 there are provided differential amplifiers 18, 19 forrespectively detecting the currents flowing into the drivingpiezo-electric section 4 of the vibration member 1 and the drivingpiezo-electric section 8 of the second vibration member 5 by amplifyingthe voltages across resistors 20, 21. In contrast to the foregoing firstembodiment in which the phase difference detector 10 is given signalsfrom the detecting piezo-electric elements 2, 6, said phase differencedetector 10 in the second embodiment is given the output signals of thedifferential amplifiers 18, 19.

More specifically, in the foregoing first embodiment, the vibrationmembers 1, 5 are provided with detecting piezo-electric elements 2, 6for detecting the vibration states of said vibration members, and thecontrol is made in such a manner as to maintain a constant relationshipbetween the phases of two detected signals. In the present embodiment,the in-flowing currents at the application of AC voltages to thepiezo-electric sections of the vibration members are detected by thedifferential amplifiers 18, 19, and the phase difference between the ACvoltages applied to the driving piezo-electric sections are socontrolled as maintain zero phase difference between the currentsflowing into said driving piezo-electric sections.

As explained in the foregoing, the present invention allows to maintainzero spatial phase difference between the travelling vibration wavesformed in a pair of vibration members supporting a sheet therebetween,even when said phase are affected for example by a change in thespecific frequency of said vibration members resulting from afluctuation in the thickness of said sheet or a change in theenvironmental conditions, thereby significantly reducing the unevennessin the sheet feeding. It is therefore rendered possible to improve theefficiency of sheet feeding, and to obtain fine beautiful image printingwhen applied for example to a facsimile apparatus.

In the foregoing embodiments, it is assumed that the spatial phases ofvibration waves in the first and second vibration members are affectedby the fluctuation in the thickness of sheet or in the environmentalconditions. However, if such fluctuation affects the spatial phases ofthe vibration of only one vibration member, it is also possible todetect the vibration wave of such affected vibration member only,thereby determining the aberration of said vibration wave from thereference position and to regulate the phase of the vibration wave ofsaid affected vibration member according to the detected amount ofaberration.

What is claimed is:
 1. A feeding device for a sheet, comprising:(a)first vibration means so arranged as to frictionally contact the sheet;(b) second vibration means opposed to said first vibration means acrosssaid sheet and so arranged as to frictionally contact said sheet; (c)first electromechanical conversion means for generating a firsttravelling vibration wave on said first vibration means in response to afirst applied electrical signal; (d) second electromechanical conversionmeans for generating a second travelling vibration wave on said secondvibration means in response to a second applied electrical signal; (e)first detecting means for generating a first electrical signalcorresponding to the state of said first travelling vibration wave; (f)second detecting means for generating a second electrical signalcorresponding to the state of said second travelling vibration wave; and(g) changing means for detecting the phase difference between said firstand second electrical signals and changing the phase of at least one ofsaid first and second applied electrical signals according to saiddetected phase difference in order to coincide the phase between thevibration wave generated in the first vibration means and that in thesecond vibration means.
 2. A feeding device according to claim 1,wherein said first detecting means is provided on said first vibrationmeans.
 3. A feeding device according to claim 2, wherein said seconddetecting means is provided on said second vibration means.
 4. A feedingdevice according to claim 3, wherein said second detecting means isprovided in a position on said second vibration means spatiallycorresponding to the position of said first detecting means on saidfirst vibration means.
 5. A feeding device according to claim 1, whereinsaid first vibration means consists of an elongated circular-shapedelastic member having a straight portion therein.
 6. A feeding deviceaccording to claim 5, wherein said second vibration means consists of anelongated circular-shaped elastic member having a straight portiontherein.
 7. A feeding device according to claim 6, wherein said sheet isso arranged as to be pinched between the straight portion of said firstvibration means and the straight portion of said second vibration means.8. A feeding device according to claim 4, wherein each of said first andsecond detecting means includes a piezoelectric element.
 9. A feedingdevice for a sheet, comprising:(a) first vibration means so arranged asto frictionally contact the sheet; (b) second vibration means opposed tosaid first vibration means across said sheet, and so arranged as tofrictionally contact said sheet; (c) first electromechanical conversionmeans for generating a first travelling vibration wave on said firstvibration means in response to a first applied electrical signal; (d)second electromechanical conversion means for generating a secondtravelling vibration wave on said second vibration means in response toa second applied electrical signal; (e) first detecting means forgenerating a first detection signal corresponding to the electricalphase of said first applied electrical signal; (f) second detectingmeans for generating a second detection signal corresponding to theelectrical phase of said second applied electrical signal; and (g)changing means for detecting the phase difference between said first andsecond detection signals, and changing the phase of at least one of saidfirst and second applied electrical signals according to said detectedphase difference in order to coincide the phase between the vibrationwave generated in the first vibration means and that in the secondvibration means.
 10. A feeding device for a sheet, comprising:(a) firstvibration means so arranged as to frictionally contact the sheet; (b)second vibration means opposed to said first vibration means across saidsheet and so arranged as to frictionally contact said sheet; (c) firstelectromechanical conversion means for generating a first travellingvibration wave on said first vibration means in response to a firstapplied electrical signal; (d) second electromechanical conversion meansfor generating a second travelling vibration wave on said secondvibration means in response to a second applied electrical signal; (e)first detecting means for generating a first control signalcorresponding to the state of said first travelling vibration wave; (f)second detecting means for generating a second control signalcorresponding to the state of said second travelling vibration wave; and(g) changing means for detecting the phase difference between said firstand second control signals and changing the phase of at least one ofsaid first and second travelling vibration waves according to saiddetected phase difference in order to coincide the phase between thevibration wave generated in the first vibration means and that in thesecond vibration means.
 11. A feeding device according to claim 10,wherein said first detecting means is provided on said first vibrationmeans.
 12. A feeding device according to claim 11, wherein said seconddetecting means is provided on said second vibration means.
 13. Afeeding device according to claim 12, wherein said second detectingmeans provided in a position on said second vibration means spatiallycorresponding to the position of said first detecting means on saidfirst vibration means.
 14. A feeding device for a sheet, comprising:(a)a first vibration member for generating a first travelling vibrationwave thereon in response to an applied electrical signal; (b) a secondvibration member opposed to said first vibration member across saidsheet and adapted for generating a second travelling vibration wavethereon in response to an applied electrical signal, said first andsecond travelling vibration waves causing a movement of said sheet; (c)detecting means for detecting the state of the travelling vibration wavein at least one of said vibration members, and generating a controlsignal corresponding to the amount of aberration from a predeterminedspatial position; and (d) correcting means for correcting the spatialposition of the travelling vibration wave of said vibration members inresponse to the control signal from said detecting means in order tocoincide the phase between the vibration wave generated in the firstvibration member and that in the second vibration member.
 15. A feedingdevice for a sheet, comprising:(a) a first vibration member forgenerating a first travelling vibration wave thereon in response to anapplied electrical signal; (b) a second vibration member opposed to saidfirst vibration member across said sheet and adapted for generating asecond travelling vibration wave in response to an applied electricalsignal, said first and second travelling vibration waves causing amovement of said sheet; (c) detecting means for detecting the state ofthe travelling vibration wave in at least one of said vibration membersand generating a control signal corresponding to the amount ofaberration from a predetermined spatial position; and (d) correctingmeans for correcting the spatial position of the travelling vibrationwave of said one vibration member in response to the control signal fromsaid detecting means in order to coincide the phase between thevibration wave generated in the first vibration member and that in thesecond vibration member.
 16. A feeding device for a sheet,comprising:(a) a first vibration member for generating a firsttravelling vibration wave thereon in response to an applied electricalsignal; (b) a second vibration member opposed to said first vibrationmember across said sheet and adapted for generating a second travellingvibration wave thereon in response to an applied electrical signal, saidfirst and second travelling vibration waves causing a movement of saidsheet; (c) detecting means for detecting the state of the travellingvibration wave in at least one of said vibration members, and generatinga control signal corresponding to the degree of deviation from apredetermined spatial position at a certain time; and (d) correctingmeans for correcting the spatial position of the travelling vibrationwaves of said vibration members in response to the control signal fromsaid detecting means in order to coincide the phase between thevibration wave generated in the first vibration member and that in thesecond vibration member.
 17. A sheet feeding device, comprising:(a) avibration member for generating a travelling vibration wave to feed asheet member, said vibration member having first and second vibrationelements provided in positions for pinching said sheet member; and (b)means for varying the phase difference between the vibration wavegenerated in the first vibration element and that in the secondvibration element according to a change in the feeding speed of saidsheet member in order to coincide the phase between the vibration wavegenerated in the first vibration element and that in the secondvibration element.